U.S. patent number 9,933,140 [Application Number 15/054,588] was granted by the patent office on 2018-04-03 for light emitting device.
This patent grant is currently assigned to NICHIA CORPORATION. The grantee listed for this patent is NICHIA CORPORATION. Invention is credited to Yasuo Fujikawa, Tomohiro Ikeda, Yohei Inayoshi, Takuya Wasa, Motokazu Yamada.
United States Patent |
9,933,140 |
Fujikawa , et al. |
April 3, 2018 |
Light emitting device
Abstract
A light emitting device includes a plurality of oblong flexible
substrates, each flexible substrate comprising a sheet-shaped base
body and a wiring pattern formed on one face of the base body, and
each flexible substrate having a plurality of light emitting
sections disposed thereon; a plurality of a reflective layers, each
reflective layer being disposed at a periphery of a respective
light emitting section above a respective flexible substrate; an
insulating reflective sheet made of a light reflecting resin, the
reflective sheet having a plurality of through holes located such
that the light emitting sections and at least a portion of the
reflective layers are exposed via the through holes; and a
plurality of adhesive members, each adhesive member adhering a
respective flexible substrate to the reflective sheet in regions
where the reflective layer is not formed.
Inventors: |
Fujikawa; Yasuo (Yokohama,
JP), Wasa; Takuya (Kaifu-gun, JP), Ikeda;
Tomohiro (Komatsushima, JP), Inayoshi; Yohei
(Komatsushima, JP), Yamada; Motokazu (Tokushima,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
NICHIA CORPORATION |
Anan-shi, Tokushima |
N/A |
JP |
|
|
Assignee: |
NICHIA CORPORATION (Anan-Shi,
JP)
|
Family
ID: |
56798175 |
Appl.
No.: |
15/054,588 |
Filed: |
February 26, 2016 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
|
US 20160252218 A1 |
Sep 1, 2016 |
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Foreign Application Priority Data
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Feb 27, 2015 [JP] |
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2015-038645 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F21V
19/005 (20130101); G02F 1/1336 (20130101); G02F
1/133605 (20130101); H01L 25/0753 (20130101); G02F
1/133603 (20130101); F21Y 2103/10 (20160801); F21Y
2105/16 (20160801); F21Y 2115/10 (20160801); H05K
2201/10106 (20130101); H05K 1/189 (20130101); F21Y
2113/00 (20130101) |
Current International
Class: |
F21V
11/00 (20150101); F21V 19/00 (20060101); H01L
25/075 (20060101); G02F 1/1335 (20060101); H05K
1/18 (20060101) |
Field of
Search: |
;362/97.1,235,609,84,341,241 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2006-332024 |
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Dec 2006 |
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JP |
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2008-003254 |
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Jan 2008 |
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JP |
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2008-227423 |
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Sep 2008 |
|
JP |
|
2009-289687 |
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Dec 2009 |
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JP |
|
2010-278016 |
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Dec 2010 |
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JP |
|
2010-278426 |
|
Dec 2010 |
|
JP |
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2011-090977 |
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May 2011 |
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JP |
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2011-165434 |
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Aug 2011 |
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JP |
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2012-203997 |
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Oct 2012 |
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JP |
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2013-037870 |
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Feb 2013 |
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JP |
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2013-152865 |
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Aug 2013 |
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JP |
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2014-131084 |
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Jul 2014 |
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JP |
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2014-167495 |
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Sep 2014 |
|
JP |
|
WO-2007/037035 |
|
Apr 2007 |
|
WO |
|
WO-2012/029686 |
|
Mar 2012 |
|
WO |
|
Primary Examiner: Franklin; Jamara
Attorney, Agent or Firm: Foley & Lardner LLP
Claims
What is claimed is:
1. A light emitting device comprising: a plurality of oblong
flexible substrates, each flexible substrate comprising a
sheet-shaped base body and a wiring pattern formed on one face of
the base body, and each flexible substrate having a plurality of
light emitting sections disposed thereon; a plurality of a
reflective layers, each reflective layer being disposed at a
periphery of a respective light emitting section above a respective
flexible substrate; an insulating reflective sheet made of a light
reflecting resin, the reflective sheet having a plurality of
through holes located such that the light emitting sections and at
least a portion of the reflective layers are exposed via the
through holes; and a plurality of adhesive members, each adhesive
member adhering a respective flexible substrate to the reflective
sheet in regions where the reflective layer is not formed.
2. The light emitting device according to claim 1, further
comprising an underlayer disposed on a portion of each of the
flexible substrates, wherein at least a portion of each underlayer
is interposed between each flexible substrate and each respective
reflective layer.
3. The light emitting device according to claim 2, wherein each of
the flexible substrates includes a region where the base body and
the wiring pattern are stacked in that order, and wherein at least
one of the flexible substrates includes, in an area above the
wiring pattern, a region where the underlayer and the reflective
layer are stacked on the wiring pattern, and a second region where
the underlayer is stacked on the wiring pattern but exposed from
the reflective layer.
4. The light emitting device according to claim 1, wherein the
flexible substrates are lined up in a direction substantially
perpendicular to a longitudinal direction of the flexible
substrates.
5. The light emitting device according to claim 1, wherein the
flexible substrates are linearly arranged along a longitudinal
direction of the flexible substrates.
6. The light emitting device according to claim 1, wherein the
reflective sheet has oblique face portions extending obliquely from
portions of the reflective sheet that are adhered to the flexible
substrates so as to spread apart from one another as they become
more distant from the light emitting sections of the flexible
substrates, the oblique face portions being disposed so as to
interpose and extend along groups of through holes that are
linearly arranged in longitudinal directions of the flexible
substrates.
7. The light emitting device according to claim 1, wherein the
reflective sheet has an oblique face portion for each of the
through holes extending obliquely from a portion of the reflective
sheet that is adhered to each flexible substrate so as to spread
apart from the rim of the through hole as it becomes more distant
from the light emitting sections of the flexible substrates.
8. The light emitting device according to claim 1, wherein the
light emitting sections have a plurality of light emitting elements
that are electrically connected to the wiring pattern via
electrodes of the light emitting elements, the flexible substrates
have a single row of wiring members extending between at least two
adjacent light emitting elements, and the at least two adjacent
light emitting elements are disposed and connected in series so
that electrodes of opposing polarities face one another.
9. The light emitting device according to claim 1, further
comprising an insulating sheet continuously adhered to the faces of
the flexible substrates opposite the faces on which the light
emitting sections are disposed, and to the same face of the
reflective sheet as that adhered to the flexible substrates.
10. The light emitting device according to claim 1, wherein (i)
faces of the flexible substrates bonded to the reflective sheet
that are opposite faces on which light emitting sections of the
flexible substrates are disposed, are adhered to (ii) faces of a
plurality of other flexible substrates opposite faces on which
light emitting sections of the other flexible substrates are
disposed.
11. The light emitting device according to claim 1, wherein the
reflective sheet has slits extending in a direction substantially
perpendicular to a longitudinal direction of the flexible
substrates, a plurality of the slits being located at positions
that deviate from the light emitting sections of the flexible
substrates.
12. The light emitting device according to claim 1, wherein a part
of each of the reflective layers overlaps with the reflective
sheet.
13. The light emitting device according to claim 1, further
comprising a plurality of underlayers, each underlayer being
located under a corresponding one of the reflective layers.
14. The light emitting device according to claim 13, wherein: each
light emitting section comprises a light emitting element, and an
upper face of each underlayer is at lower than an upper face of
each corresponding light emitting element.
15. The light emitting device according to claim 13, wherein: each
light emitting section comprises a light emitting element, and a
distance between each reflective layer and each corresponding light
emitting element is greater than a distance between each underlayer
and each corresponding light emitting element.
16. The light emitting device according to claim 1, wherein the
reflective layers are separated from one another based on a
configuration of the light emitting sections.
17. The light emitting device according to claim 1, wherein the
reflective layers are separated from one another based on a number
of light emitting sections.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. .sctn. 119
to Japanese Patent Application No. 2015-038645 filed Feb. 27, 2015,
the contents of which are incorporated herein by reference in their
entirety.
BACKGROUND
The present disclosure relates to a light emitting device that
includes a flexible substrate.
A light emitting device employing a flexible substrate that
includes a reflective film covering a wiring pattern disposed on
the sheet base material has been proposed. For example, Japanese
Unexamined Patent Application Publication No. 2014-131084 (Patent
Document 1) discloses, as an example of the reflective film, an
insulating white ink referred to as a white resist made of a
silicone-based resin containing a titanium oxide.
Japanese Unexamined Patent Application Publication No. 2010-278016
(Patent Document 2) discloses an electronic device constructed by
securing an LED substrate to a metal sheet support using substrate
holders, the LED substrate having a plurality of LEDs mounted on
one face and a reflective sheet made of a synthetic resin having
through holes at the positions corresponding to the LEDs.
SUMMARY
The light emitting device according to one embodiment comprises a
plurality of oblong flexible substrates each including a wiring
pattern disposed on one face of a sheet-shaped base body, light
emitting sections disposed on the flexible substrates, a reflective
layer disposed at the peripheries of said light emitting sections
directly on the wiring pattern or spaced apart from said wiring
patterns in the stacking direction on the flexible substrates, an
insulating reflective sheet made of a light reflecting resin
including through holes so as to expose the light emitting sections
and at least one portion of the reflective layer, and an insulating
adhesive member adhering the flexible substrates to the reflective
sheet in the regions where said reflective layer is not formed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic plan view of the light emitting device
according to Embodiment 1.
FIG. 2 is a schematic bottom view of the light emitting device
according to Embodiment 1.
FIG. 3 is a schematic plan view of the light emitting device
according to Embodiment 1 enlarging the region III indicated in
FIG. 1.
FIG. 4 is a schematic cross-sectional view of the light emitting
device according to Embodiment 1 viewed in the direction indicated
by arrows IV-IV in FIG. 3.
FIG. 5 is a schematic plan view of the flexible substrate of the
light emitting device according to Embodiment 1, illustrating one
example of the wiring member formed under the reflective layer and
an underlayer.
FIG. 6 is a schematic view of the flexible substrate of the light
emitting device according to a variation of Embodiment 1,
illustrating one example of the wiring member formed under the
reflective layer and the underlayer.
FIG. 7A is a schematic view showing a production step for the light
emitting device according to Embodiment 1, which is a plan view of
the reflective sheet.
FIG. 7B is a schematic view showing a production step for the light
emitting device according to Embodiment 1, which is a bottom view
of the reflective sheet to which an adhesive member has been
pasted.
FIG. 7C is a schematic view showing a production step for the light
emitting device according to Embodiment 1, which is a plan view of
the reflective sheet which has undergone cutting and hole-making
machining operations.
FIG. 7D is a schematic view showing a production step for the light
emitting device according to Embodiment 1, which is a bottom view
of the reflective sheet to which flexible substrates have been
adhered.
FIG. 8A is a schematic cross-sectional view of a lighting device
including the light emitting device according to Embodiment 1.
FIG. 8B is a schematic cross-sectional view of a lighting device
including the light emitting device according to Embodiment 2.
FIG. 8C is a schematic cross-sectional view of a lighting device
including the light emitting device according to a variation of
Embodiment 2.
FIG. 9 is a schematic bottom view of the light emitting device
according to Embodiment 3.
FIG. 10 is a schematic bottom view of the light emitting device
according to Embodiment 4.
FIG. 11A is a schematic plan view of the reflective sheet used in
the light emitting device according to Embodiment 5.
FIG. 11B is a schematic plan view of the light emitting device
according to Embodiment 5.
FIG. 11C is a schematic exploded perspective view showing a stack
of a plurality of light emitting devices according to Embodiment
5.
FIG. 12 is a schematic exploded perspective view of the light
emitting device according to Embodiment 6 viewed from the side
opposite the emission surface.
FIG. 13 is a schematic plan view of a flexible substrate of the
light emitting device according to a variation of Embodiment 6,
showing an example of the wiring pattern formed under the
reflective layer and the underlayer.
FIG. 14 is a schematic view showing a production step for the light
emitting device according to the variation of Embodiment 6, which
is a plan view of a collective sheet for the flexible substrates
before separating.
FIG. 15 is a schematic view of the light emitting device according
to Embodiment 7, which is a plan view of the reflective sheet
viewed from the rear face side.
FIG. 16 is a schematic view of the light emitting device according
to Embodiment 7, which is an enlarged cross section viewed in the
direction indicated by arrows XVI-XVI in FIG. 15.
FIG. 17 is a schematic plan view of the light emitting device
according to Embodiment 8.
DESCRIPTION
Embodiments of the invention will be described below with reference
to the drawings. The following embodiments, however, exemplify the
light emitting devices for the purpose of embodying the technical
concepts of the invention, and do not limit the invention. The
dimensions, materials, and shapes of the constituent elements, as
well as the relative positioning thereof, described in the
embodiments are offered to merely as examples, and are not intended
to limit the scope of the invention to those described unless
otherwise specifically noted. The sizes of the components, their
positional relationship, or the like, shown in the drawings might
be exaggerated for clarity of explanations.
Embodiment 1
As shown in FIGS. 1 and 4, the light emitting device 1 according to
Embodiment 1 includes a plurality of oblong flexible substrates 10
(hereinafter referred to as flexible substrates 10), reflective
sheet 20, and adhesive members 30. A plurality of light emitting
sections 2 and a reflective layer 8 are disposed at the peripheries
of the light emitting sections 2 on the flexible substrates 10. As
shown in FIG. 1, the light emitting device 1 is provided with a
plurality of flexible substrates 10 (six shown here) disposed at a
certain pitch P1 along the direction perpendicular to the
longitudinal direction of the flexible substrates. Each flexible
substrate 10 is provided with a plurality of light emitting
sections 2 (nine shown here) disposed at a certain pitch P2 along
the longitudinal direction of the substrate. As shown FIG. 1, at
one end of the upper faces 15 of the flexible substrates 10 (the
left end in FIG. 1), connectors 3 and 4 are mounted for
electrically connecting an external power supply to a wiring
pattern 13 shown FIG. 4 via a wire harness, for example. The
reflective sheet 20 has through holes 21 so as to expose the light
emitting sections 2 and at least one portion of the reflective
layers 8. The reflective sheet 20 also has through holes 22 to
expose the connectors 3 and 4. The upper faces 15 of the flexible
substrates 10 are adhered to the rear face 26 of the reflective
sheet 20 shown FIG. 2 via the adhesive members 30 shown FIG. 4. The
light reflecting surface (the face of the opposite to the rear
face) of the reflective sheet 20 may be referred to as the front
face 25 hereinafter.
By disposing the insulating reflective film on the wiring pattern,
the light emitting device 1 can reduce electric shocks when the
device is powered, and protect against static electricity when the
device is handled, as well as improving the light reflectance of
the substrate surface. The use of the white resist as a reflective
film, however, may be costly, and there may be a need for further
cost reduction.
By including the reflective sheet, the light emitting device
disclosed in Patent Document 2 can reflect the LED light. However,
the LED substrate and the reflective sheet are secured to the
support using substrate holders, which may make it difficult to
produce a flexible light emitting device.
An object of certain embodiments of the present invention is to
provide a low-cost bendable light emitting device.
According to the light emitting devices of certain embodiments, a
bendable light emitting device can be produced at low cost by
adhering flexible substrates to a reflective sheet.
Flexible Substrate
The flexible substrates 10 are disposed on the reflective sheet 20
with light emitting elements 5 shown in FIG. 4 and other components
mounted thereon. The pitch P1 between the flexible substrates 10 is
set larger than the width of a flexible substrate 10. The flexible
substrates 10 can be flexible printed boards having a wiring
pattern on at least one face of a sheet-shaped base body 11.
Each flexible substrate 10, as shown in FIG. 4, has a region where
the base body 11 and the wiring member 13 (wiring pattern) are
stacked in that order. On the wiring pattern 13, a region where an
underlayer 7, which be used as a base for the reflective layer 8,
alone is stacked, and a region where both the underlayer 7 and the
reflective layer 8 are stacked. An adhesive layer 12 may be
disposed between the base body 11 and the wiring pattern 13. In the
explanation below, the face of a flexible substrate 10 on which the
wiring pattern 13 is formed may be referred to as the upper face 15
(see FIG. 1), and the face on the base body 11 side may be referred
to as the back face 16 (see FIG. 2).
The base body 11 is the base of the flexible substrate 10, and is
made of a flexible insulating material. Polyimide, for example, is
a suitable material for the base body 11. A molded reinforced
plastic material made by pre-impregnating a fibrous material, such
as glass cloth or carbon fiber fabric, with a resin (e.g., glass
fiber reinforced epoxy composite, prepreg, or the like) is also
suitable. A resin film, such as polyethylene terephthalate (PET),
polyethylene naphthalate, polyetherimide, polyphenylene sulfide,
liquid crystal polymer, or the like, may also be used. The
thickness of the base body 11 is, for example, in a range between
about 10 and 300 .mu.m. The base body 11 may be of either a single
layer or multilayer structure.
The adhesive layer 12 adheres the base body 11 and the wiring
pattern 13. As material for the adhesive layer 12, examples include
a urethane-based adhesive, or the like. The adhesive layer 12 may
not be required in the case where the base body 11 is made of a
material capable of directly adhering to the wiring pattern 13 such
as a molded reinforced plastic material mentioned above, for
example. In these cases, the wiring member 13 is formed directly on
the base body 11.
The wiring pattern 13 includes a conductive material. The wiring
pattern 13 is formed on the base body 11, for example, via an
adhesive layer 12, which creates an electrical circuit when
electrically connected to each light emitting element 5. The wiring
member 13, for example, is made of a copper foil. Besides that, an
aluminum foil, aluminum alloy foil, stainless steel foil, or the
like, can also be employed. The thickness of the wiring pattern may
be in a range between 10 .mu.m and 50 .mu.m.
As shown in FIGS. 3 and 4, a groove extending in the longitudinal
direction of the flexible substrate 10 is formed between two lines
of wiring member 13a and 13b which make up the wiring pattern 13
formed on the flexible substrate 10. The groove can be formed by
removing the material forming the wiring pattern 13 formed on the
flexible substrate 10 by etching or the like.
As shown in FIG. 5, each of the two wiring members 13a and 13b is
formed in a linear shape along a direction that is substantially
parallel to the longitudinal direction of the flexible substrate
10. The width of the flexible substrate 10 is denoted as W1, and
the width of each of the two wiring members 13a and 13b is denoted
as L1. The width from an edge of each of the wiring members 13a and
13b to the outer edge of the base body 11 (hereinafter referred to
as the creepage distance) is denoted as L2, and the gap between the
two wiring members 13a and 13b is denoted as L3. In this case,
preferably, the relationship expressed by the following formula (1)
is established. W1=2.times.L1+2.times.L2+L3 formula (1)
The widths L1 to L3 can suitably be selected in accordance with the
purpose and application. For example, in the case where the light
emitting device will be installed in a backlight for a television,
the widths L1, L2, and L3 can be set, for example, to 6 mm, 2 mm,
and 200 .mu.m, respectively.
As shown in FIGS. 3 and 4, each light emitting element 5 is
disposed on the gap (groove) between the two wiring members 13a and
13b. Two adjacent light emitting elements 5 are disposed so that
electrodes of the light emitting elements having the same polarity
adjacent each other in the longitudinal direction of the flexible
substrate 10 and are connected in parallel.
Light Emitting Section 2
As shown in FIGS. 3 and 4, the light emitting element 5 is
electrically connected to the wiring member 13. As shown in FIG. 1,
the pitch P2 for arranging the light emitting sections 2 on the
flexible substrates 10 may be set larger than the width of a
flexible substrate 10. The pitch P2 may be different from, or the
same as, the pitch P1 described above. Here, as one example, the
pitch P2 is the same as the pitch P1. The light emitting section
2s, as shown in FIGS. 3 and 4, can include the light emitting
element 5 and a sealing member 6 respectively.
Light Emitting Element
The light emitting elements 5 emit light when a prescribed voltage
is applied. An emission wavelength of the light emitting elements 5
can be visible, ultraviolet, or infrared light, or the like.
In the case where using the light emitting elements emit visible
light, the emission color can be any of blue, green, and red light,
for example.
A white light emitting element such as a blue light emitting
element coated with a fluorescent material can also be used.
The semiconductor materials used in the light emitting element 5
can be any compound semiconductor, such as group III-V, group
II-VI, or the like.
The light emitting elements 5 may be flip chip mounted or face-up
mounted on the wiring member 13. As shown in FIGS. 3 and 4, in the
case of using flip chip mounting, the p-side electrode (i.e. anode)
and the n-side electrode (i.e. cathode) of each light emitting
element 5 are bonded to a pair of wiring members 13a and 13b,
respectively, via a pair of conductive joining material. For the
conductive joining material, an Sn--Ag--Cu-based, Sn--Cu-based, or
Au--Sn-based solder, Au metal bump, Ag paste, or the like, can be
used.
In the case of using face-up mounting manner, each light emitting
element 5 may be bonded on the base body 11 and/or the wiring
member 13 by an insulating joining material, such as a resin, or
any of the conductive joining materials mentioned above, and
electrically connected to the wiring pattern 13 by wires. In the
case where the element substrate of the light emitting element 5 is
conductive, one of the electrodes is electrically connected to the
wiring member 13a or 13b using any of the aforementioned conductive
joining materials, while the other electrode is electrically
connected to another wiring member 13a or 13b using a wire.
Sealing Member
The sealing member 6, as shown in FIGS. 3 and 4, encloses and
protects the light emitting element 5. The sealing member 6 is
light transmissive. The sealing member 6 may be provided on the
upper face of the flexible substrate 10 so as to cover the light
emitting element 5. The viscosity of the material forms the sealing
member 6 can be adjusted so as to be applicable by printing or by
using a dispenser, for example. The sealing member 6 can be cured
by way of heat treatment or UV light irradiation. The sealing
member 6 preferably has good adhesion with the flexible substrate
10 and the light emitting element 5. Also, the sealing member 6
preferably has flexibility. The emission wavelength and light
distribution characteristics of the light emitting device can be
adjusted by containing wavelength conversion material such as a
YAG-based, TAG-based, or silicate-based phosphor, or the like in
the sealing, member 6. Also, an inorganic light diffusing material,
such as titanium oxide, silicon oxide, alumina, zinc oxide, fine
glass powder, or the like; or an organic light diffusing material,
such as acrylic, polystyrene, or the like can be contained in the
sealing member 6. The sealing member 6 preferably has a convex
shape from the perspective of improving light extraction efficiency
as shown in FIG. 4. The shape of the sealing member 6 can be an
approximate hemispherical shape, an oblong convex shape in a
cross-sectional view, a circular or elliptical shape in a plan
view, for example.
Connector 3 and 4
The connectors 3 and 4 are disposed in correspondence to the
positive and negative polarities and disposed on the wiring pattern
13. Metal terminals such as DF59M manufactured by Hirose Electric
Co., Ltd., or molded metal terminals, such as DF61 manufactured by
Hirose Electric Co., Ltd., can be used as the connectors 3 and
4.
The p-side electrode of the light emitting element 5 is
electrically connected to the connector 3 via the wiring member
13a, and is electrically connected to the positive terminal of an
external power supply via a wire harness, for example.
The n-side electrode of the light emitting element 5 is
electrically connected to the connector 4 via the wiring member
13b, and is electrically connected to the negative terminal of an
external power supply via a wire harness, for example.
Examples of materials of the connectors 3 and 3 include rustproofed
copper with tinning plating. Examples of methods of joining the
connectors 3 and 4 with the wiring pattern 13 include reflow
soldering, ultrasonic bonding, resistance welding, crimping, or the
like.
Underlayer 7
The underlayer 7 is used as the base for the reflective layer 8. As
shown in FIGS. 3 and 4, an underlayer 7 is disposed on the flexible
substrate 10. The underlayer 7 preferably covers the wiring member
13 and/or the base body 11 or the adhesive layer 12 partially or
entirely, while exposing a portion of the wiring member 13. The
underlayer 7 has openings (for example, a circular shape) for
exposing a pair of wiring members 13a and 13b which correspond to a
pair of positive and negative polarities, and the groove between
the pair of positive and negative wiring members 13a and 13b. The
size of the opening is preferably formed in the minimum size
required to enable the electrical connection between the light
emitting element 5 and the wiring pattern 13 within the opening.
The openings may have different in shape and size each other, but
are preferably the same in shape and size.
The underlayer 7 can include a thermosetting resin, thermoplastic
resin, or the like, for example. Specific examples include modified
epoxy resin compositions, such as epoxy resin compositions,
silicone resin compositions, silicone modified epoxy resins, and
the like; modified silicone resin compositions, such as epoxy
modified silicone resins, or the like; polyimide resin
compositions, modified polyimide resin compositions; polyphtalamide
(PPA); polycarbonate resins; polyphenylene sulfide (PPS); liquid
crystal polymers (LCP); ABS resins; phenol resins; acrylic resins;
PBT resins, or the like.
The underlayer 7 preferably contains a material that reflects the
light emitted from the light emitting element 5, as well as the
light whose wavelength has been converted by the wavelength
conversion material. The reflectance here with respect to the light
described is preferably 60% or higher, more preferably 65% or
higher, or 70% or higher. Examples of such materials include
light-reflecting materials. Examples of light-reflecting materials
include titanium dioxide, silicon dioxide, zirconium dioxide,
potassium titanate, alumina, aluminum nitride, magnesium oxide,
boron nitride, mullite, niobium oxide, and various rare earth
oxides (for example, yttrium oxide and gadolinium oxide). The
underlayer 7 may contain additives, including fibrous fillers, such
as glass fibers and wollastonite, carbon, talc, and inorganic
fillers such as silicon oxide, or the like. The content of these
materials can be in a range between 5 and 50 weight percent
relative to the total weight of the underlayer 7.
The underlayer 7 is preferably formed in the thickness so that its
upper face is lower than the upper face of the light emitting
element 5. The underlayer 7 preferably has a thickness which does
not undermine the flexibility of the flexible substrate 10, and can
be formed, for example, in thickness of about 1 to 50 .mu.m. The
underlayer 7 can be formed on one face of the base body by
printing, potting, spin coating, dipping, or the like.
Reflective Layer 8
The reflective layer 8, as shown in FIGS. 3 and 4, is disposed on
the upper face of the wiring pattern 13, particularly in the
vicinity of the light emitting section 2, that is the region
corresponding to the through hole 21 or the opening of the
reflective sheet 20, to increase the light extraction efficiency of
the light emitting device 1. In this embodiment, the reflective
layer 8 is formed in an annular shape in a plan view, disposed over
the flexible substrate 10 spaced apart from the wiring pattern 13
in the stacking direction by the interposed underlayer 7.
The reflective layer 8 is preferably disposed, for example, in the
form of islands (that is, a plurality of separated reflective
layers are disposed) in correspondence with the quantity of the
light emitting elements 5 disposed on the flexible substrates 10.
The reflective layer 8 is preferably formed as islands that are
separated from one another. For example, The reflective layer 8
formed as islands may be separated based on the configuration of
the light emitting section 2, or based on the number of light
emitting sections 2.
As shown in FIGS. 3 and 4, an edge of the reflective layer 8 on the
light emitting section 2 side (that is, an edge facing the opening)
is preferably more distant from the light emitting section 2 than
the edge of the underlayer 7 on the light emitting section 2 side.
In this case, the distance between the edge of the reflective layer
8 closer to the light emitting section 2 and the edge of the
underlayer 7 closer to the light emitting section 2 is from about
0.1 to 0.5 mm, for example. An area of the opening in the
reflective layer 8 can be between about 0.8 and 2.5 times,
preferably between about 1 and 2 times, more preferably between
about 1.3 and 1.6 times, of an area of the opening in the
underlayer 7.
The reflective layer 8 can be formed from any of the materials for
the underlayer 7 mentioned above. In other words, the reflective
layer 8 can be formed using, for example, a thermosetting resin,
thermoplastic resin, or the like. Furthermore, it is preferable for
these resins to contain a light-reflecting material and/or other
additives. The reflective layer 8 preferably has the light
reflectance of 80% or higher with respect to the light from the
light emitting element as well as the light whose wavelength has
been converted by wavelength conversion material. It is preferable
for the reflective layer 8 to have a higher light reflectance than
the underlayer 7. The reflective layer 8 can contain the
light-reflecting material and/or other additives in the ratio of
from 5 to 70 weight percent to the total weight of the reflective
layer 8. The reflective layer 8, however, preferably contains the
same materials or have the same composition as the underlayer 7.
The light reflectance of the reflective layer 8 mentioned above is
preferably higher than that of the underlayer 7. For this purpose,
the reflective layer 8 preferably contains a light-reflecting
material having a higher light reflectance than that contained in
the underlayer 7 and/or contains a larger amount of the
light-reflecting material.
By forming the reflective layer 8 on the underlayer 7, the role of
protecting the wiring member 13 by ensuring the insulating
properties of the flexible substrate 10 and the role of increasing
the light extraction efficiency by preventing the light emitted
from the light emitting elements 5 from being absorbed by the
substrates can be separated. More particularly, with this
arrangement, even though the adhesion to the sealing member 6 and
the light reflectance of the under layer 7 and the reflective layer
may be contrary properties, having the underlayer 7 and the
reflective layer 8 play different roles as described above can
attain a balance between the adhesion and light reflectance
properties.
The thickness of the reflective layer 8 can be suitably set within
the ranges discussed in connection to the thickness of the
underlayer 7. The thickness of the reflective layer 8 is preferably
substantially the same as that of the underlayer 7. The thickness
of the reflective layer 8 is more preferably set to achieve enough
light reflectance in accordance with the materials, particularly
the type and the content of the light-reflecting material, used to
compose the reflective layer 8. The reflective layer 8 can be
formed separately from the underlayer 7 on one face of the base
body 11 by using any of the methods mentioned in connection with
the forming method for the underlayer 7.
Reflective Sheet 20
The reflective sheet 20 is provided to reflect the light from the
light emitting sections 2 to improve the effectiveness in
extracting the light from the light emitting device 1. The
reflective sheet 20 is an insulating sheet having light
reflectance, and is preferably aflame retardant sheet. The
reflective sheet 20 is preferably a film including a synthetic
resin, for example, a white polyethylene terephthalate (white PET)
or a white glass fiber reinforced epoxy composite.
The size (that is, vertical and horizontal lengths in plan view),
and the thickness of the reflective sheet 20 are not particularly
limited, as long as it has a large enough area for disposing the
flexible substrates 10 at a proper pitch required for the finished
product of the light emitting device 1 thereon. Its size can be
suitably selected in accordance with the purpose. For example, in
the case where the light emitting device is used for a television
backlight application, the vertical and horizontal lengths may be
several tens of centimeters or larger. In this case, the thickness
of the reflective sheet 20 may be in a range between about several
tens and several hundreds of micrometers. Any commercially
available PET film used as an LCD backlight reflective sheet (for
example, the white low specific gravity grade (E6SR) of
Lumirror.TM., 188 .mu.m in thickness, high reflectance type
(product number 188) manufactured by Toray Industries, Inc., or the
like) can be employed as the reflective sheet 20.
Adhesive Member 30
The adhesive member 30 adheres the flexible substrates 10 and the
reflective sheet 20 in the regions where the reflective layer 8 is
not formed. The adhesive member 30 preferably has insulating
properties, and furthermore, preferably has high flame retardancy.
A double-sided tape (pressure sensitive adhesive member) or the
like can be preferably used as the adhesive member 30. For example,
an acrylic-based double-sided tape manufactured by DIC Corporation
(product number 8606TN), or the like can be used. Also, a
thermosetting or thermoplastic resin liquid adhesive, or a hot melt
adhesive sheet can be also used for the adhesive member 30.
Method for Producing a Light Emitting Device Next, a method for
producing the light emitting device 1 will be explained.
First, as shown in FIG. 7A, a reflective sheet 20 is prepared. The
reflective sheet 20 is larger than the outer shape of the light
emitting device 1. The reflective sheet 20 in this embodiment is
horizontally oblong, having a vertical length that is substantially
equivalent to the finished product height of the light emitting
device 1.
Next, as shown in FIG. 7B, adhesive members 30 are disposed on the
rear face 26 of the reflective sheet 20. In this embodiment, the
adhesive members 30 have a length that is longer than the length of
the flexible substrates 10, and substantially the same width as
that of the flexible substrates 10. The adhesive members 30 in this
embodiment are acrylic-based double-sided tape. A plurality of
adhesive members 30 (six shown here) are arranged at a certain
pitch in the direction substantially perpendicular to the
longitudinal direction of the reflective sheet 20, and disposed on
the reflective sheet 20.
Next, as shown in FIG. 7C, through holes 21 and 22 are created in
the reflective sheet 20, and the reflective sheet 20 is cut to a
width of the finished product (the light emitting device 1). The
through holes 21 and 22 are preferably created simultaneously when
the reflective sheet 20 is cut to size. Here, the positions of the
through holes 21 are matched to the positions of the light emitting
sections 2 disposed on the flexible substrates 10 which will be
disposed. The positions of the through holes 22 are matched to the
positions of the connectors 3 and 4 of the flexible substrates 10.
The through holes 21 and 22 are formed so as to penetrate through
both the reflective sheet 20 and the adhesive members 30.
Then, as shown in FIG. 7D, the flexible substrates 10 are adhered
to the rear face 26 of the reflective sheet 20. The flexible
substrates 10 are aligned so that the light emitting sections 2
disposed on the faces of the flexible substrates 10 opposite the
back faces 16 are exposed at the through holes 21 of the reflective
sheet 20. On the upper face 15 side of the flexible substrates 10,
the underlayer 7 at the peripheries of the light emitting sections
2 adheres to the reflective sheet 20 via the adhesive members 30.
Also, the flexible substrates 10 are arranged so that the
connectors 3 and 4 disposed on each of flexible substrates 10 are
all aligned at one side. This can simplify the connection structure
between an external power supply and the connectors 3 and 4.
The light emitting device 1 according to this embodiment includes a
plurality of flexible substrates 10 lined up at a prescribed pitch
and adhered to the reflective sheet 20 having a larger area than
the flexible substrates. Thus, the insulating properties of the
flexible substrates 10 can be ensured by the reflective sheet 20.
Moreover, the light extraction efficiency of the light emitting
device 1 can be increased by disposing the reflective sheet 20 and
reducing an amount of the light absorbed by the flexible substrates
10,
In the light emitting device 1, moreover, the reflective sheet 20
integrated with the flexible substrates 10 can be deemed as a large
device substrate. The light emitting device 1 having such a large
area device substrate may not require the use of an insulating
white ink, referred to as white resist above, in many regions of
reflective sheet 20 where no flexible substrates 10 are adhered,
preferably the regions accounting for more than one half of the
reflective sheet. Therefore, the amount of insulating white ink
used in the light emitting device lean be reduced. Accordingly, a
bendable large area light emitting device 1 can be produced
inexpensively.
Furthermore, as shown in FIG. 4, the light emitting sections 2
including the light emitting elements 5 mounted on the flexible
substrates 10 and covered by the convex sealing member 6 may have
light distribution characteristics of high light intensity over a
wide angle region as compared to, for example, a light emitting
device having a package with a recess for light emitting elements
disposed Accordingly, the light emitting device 1 having a
two-dimensional array of light emitting sections 2 lined up at
certain intervals can be a surface emission light source having a
wide light distribution angle, which can be a suitable device for a
lighting device, such as a backlight.
Variation of Embodiment 1
As shown in FIG. 6, the light emitting device according to a
variation of Embodiment 1 has a differently shaped wiring pattern
13 on the flexible substrate 10A from that of the light emitting
device 1 according to Embodiment 1. The flexible substrate 10A has
wiring members 13a, 13b, 13c (collectively wiring member 13), which
arranged along the longitudinal direction of the flexible substrate
10. Two light emitting sections 2 are disposed between two of these
three wiring members 13a, 13b, 13c, respectively. The grooves
between the wiring members 13 extend in the direction perpendicular
to the longitudinal direction of the flexible substrate 10A. The
two adjacent light emitting sections 2 (light emitting elements 5)
are disposed so that these electrodes having opposing polarities
face to each other in the longitudinal direction of the flexible
substrates 10A and connected in series.
As shown in FIG. 6, the width of the flexible substrate 10A is
denoted as W2. The width of the wiring members 13 formed in one
line in the longitudinal direction of the flexible substrate 10A is
denoted as L1, and the creepage distance is denoted as L2. In this
case, preferably, the relationship expressed by the following
formula (2) is established. The groove width between the wiring
members 13a and 13b, and between the wiring members 13b and 13c, is
denoted as L3. W9=L1+2.times.L2 formula (2)
Either the connector 3 or 4 in this variation may be placed at the
left end, and the other at the right end, of the flexible
substrates 10A, as shown FIG. 14. At every groove between the
wiring members 13, one piece of light emitting element 5 may be
electrically connected to a pair of wiring members 13 interposing
the groove (for example, a pair of the wiring members 13a and 13b,
a pair of the wiring members 13b and 13c in FIG. 6).
According to this variation, the width W2 of the flexible substrate
10A can be made narrower than the width W1 of the flexible
substrate 10. This may reduce the amount of substrate material
required and production costs.
Embodiment 2
When the light emitting device 1 is used as a direct-lit type
backlight or a lighting device, for example, as shown in FIG. 8A, a
light diffuser plate (light irradiation plate) 40, which is
installed in front of the light emitting device 1 at a prescribed
distance may be used. FIG. 8A schematically shows across section of
the light emitting device 1 according to Embodiment 1 cut at the
positions of the light emitting sections 2 on the flexible
substrates 10 when viewed from the side where the connectors 3 and
4 are located (the left hand side in FIG. 1).
As shown in FIG. 8A, a region 41 of the light diffuser plate 40
substantially equidistant from two adjacent flexible substrates 10
may tend to have lower intensity of light from the light emitting
sections 2 of the light emitting device 1.
The light emitting device 1B according to Embodiment 2, as shown in
FIG. 8B, differs from the light emitting device 1 according to
Embodiment 1 by having a reflective sheet 20B that is
three-dimensionally formed. The reflective sheet 20B has through
holes 21 as in the case of the reflective sheet 20, but is not flat
overall, and has a plurality of three-dimensionally structured
sections.
More specifically, the reflective sheet 20B has oblique face
portions 27 which extend obliquely so as to spread apart as they
become perpendicularly (upwardly) more distant from the light
emitting sections 2 of the flexible substrates 10. The oblique face
portions 27 shown in FIG. 8B are provided an as to interpose each
through hole group comprising the through holes 21 linearly
arranged in the longitudinal direction of the flexible substrates
10 from both sides along the longitudinal direction of the flexible
substrates 10. The reflective sheet 20B, moreover, has flat
portions 27B between two oblique face portions 27 provided in the
spaces between two adjacent flexible substrates 10.
The oblique face portions 27 can be formed by bending or vacuum
forming the flat reflective sheet 20. The oblique face portions 27
of the reflective sheet 20B provided between the flexible
substrates 10 may allow the light emitting device 1B to adjust the
distribution of the LED light. In other words, the light
transversely emitted from the light emitting sections 2 mounted on
the flexible substrates 10 can be directed towards the regions 41
of the light diffuser plate 40 which may tend to have lower
intensity of light, efficiently utilizing the light emitted in a
direction transverse to the optical axis.
Furthermore, the reflective sheet 20B having the oblique face
portions 27 will virtually have increased emission points, that is,
portions of the oblique face portion 27 which reflect the light
from the light emitting sections 2 can be regarded as additional
emission points, thereby allowing the light emitting device 1B to
reduce the unevenness of illuminance at the light diffuser plate
40. This can reduce grainy appearance (granular appearance) caused
by the so-called spots of light, which are the centers (forward
direction) of the light emitting sections 2 where the light
intensity is high, occurring especially when the light emitting
device 1B is used in a thin direct-lit backlight or lighting
device.
A size, angle, and location of the oblique face portions 27
described above can be suitably determined in accordance with the
design of the light emitting device 1. For example, assuming that
the light intensity of the optical axis direction (0 degree
direction) of the light emitting section 2 is 100%, they are
preferably set so as to result in light intensity of at least 30%
in an 80 degree direction measured from the optical axis of the
light emitting section 2.
The oblique face portions 27 described above can be any shape as
long as they can be used as a reflector to reflect the light
transversely emitted from the light emitting sections 2 upwardly.
For example, as shown in FIG. 8C, they may be configured as in the
case of the light emitting device 1C according to a variation of
Embodiment 2. In other words, in the light emitting device 1C, the
oblique face portions 27 are provided so as to interpose each
through hole group consisting of the through holes 21 linearly
arranged in the longitudinal direction of the flexible substrates
10 from both sides along the longitudinal direction of the flexible
substrates 10, and two oblique face portions 27 located between two
adjacent flexible substrates 10 are continuously formed. The light
emitting device 1C, as in the case of the light emitting device 1B,
can efficiently utilize the light emitted in the direction
transverse to the optical axis, and reduce the unevenness of
illuminance at the light diffuser plate 40.
In the above-described light emitting devices 1B and 1C, the
oblique face portions 27 are disposed so as to reflect the light
emitted from a plurality of light emitting sections 2 disposed in a
row on each of the flexible substrates 10. Alternatively, the
oblique face portions may be disposed to reflect the light from
individual light emitting sections 2. More specifically, the light
emitting device may include a reflective sheet having a ring-shaped
oblique face portion provided so as to surround at the periphery of
each light emitting section 2. In other words, each oblique face
portion may extend obliquely so as to spread out from the rim of
each through hole 21 of the reflective sheet 20 as it becomes
perpendicularly more distant from the face of the flexible
substrate 10 on which the light emitting sections 2 are
disposed.
Embodiment 3
As shown in FIG. 9, the light emitting device 1D according to
Embodiment 3 differs from the light emitting device 1 according to
Embodiment 1 by having a reflective sheet 20D that having a
circular shape in plan view. In the light emitting device 1D, a
plurality of flexible substrates 10 (five shown here--10a, 10b,
10c, 10d, and 10e) are adhered to the rear face 26 of the
reflective sheet 20D in a stripe pattern at a pitch. The flexible
substrate 10c located in the center of the reflective sheet 20D is
set to the largest length, the flexible substrates 10a and 10e
located near the edge are set to the smallest length, and the
flexible substrates 10b and 10d positioned in between are set to
the middle length.
The light emitting device 1D can be produced in similar process to
in the case of the light emitting device 1, such as creating
through holes 21 and 22 in an unprocessed reflective sheet 20 in
alignment with the positions of the light emitting sections 2 and
connectors 3 and 4, respectively, of the flexible substrates 10,
and achieving the reflective sheet 20D by cutting in accordance
with the finished product shape of the light emitting device 1D
(that is, a circular shape).
Embodiment 4
Another embodiment having a different reflective sheet shape will
be explained next.
As shown in FIG. 10, the light emitting device 1E according to
Embodiment 4 differs from the light emitting device 1 according to
Embodiment 1 by having a narrow line shape reflective sheet 20E. In
the light emitting device 1E, a plurality of flexible substrates 10
(four shown here) are arranged linearly along the longitudinal
direction of the flexible substrates 10 at a prescribed pitch, and
adhered to the rear face 26 of the reflective sheet 20E.
The light emitting device 1E can be produced in similar process to
in the case of the light emitting device 1, such as creating
through holes 21 and 22 in an unprocessed reflective sheet 20 in
alignment with the positions of the light emitting sections 2 and
connectors 3 and 4, respectively, of the flexible substrates 10,
and achieving the reflective sheet 20E by cutting in accordance
with the finished product shape of the light emitting device
1E.
Embodiment 5
In the case where the light emitting device 1 according to
Embodiment 1 is used in a backlight for a television, for example,
the vertical and horizontal lengths of the light emitting device 1,
i.e., the vertical and horizontal lengths of the reflective sheet
20, may be at least several tens of centimeters, exceeding one
meter in some cases. A packaging cost required for the light
emitting device 1 tends to easily increase as the area of the light
emitting device 1, or the reflective sheet 20, increases. For
reducing the packaging cost, the light emitting device 1F according
to Embodiment 5, as shown in FIGS. 11A and 11B, differs from the
light emitting device 1 according to Embodiment 1 by having a
reflective sheet 20F which is provided with ancillary sections 28
for packaging purposes.
The ancillary sections 28 are provided at the periphery of the part
that actually functions as the light emitting device 1. For this
purpose, the reflective sheet 20F is formed in a slightly larger
size than that of the reflective sheet 20 of the light emitting
device 1 according to Embodiment 1. The reflective sheet 20F
includes the reflective sheet 20 of the light emitting device 1 in
the center, and has the ancillary sections 28 at the four sides of
the rectangle reflective sheet 20 provided along cutting guide
lines 28L by providing cut off lines like broken-line in the
reflective sheet 20F for separating the reflective sheet 20 and the
ancillary section 28 later. Here, the ancillary sections 28 are
configured as four roughly narrow rectangular parts along the
cutoff lines 28L, and through holes 29 are created at four
corners.
The process for producing the light emitting device 1F differs from
that for the light emitting device 1 such that a reflective sheet
larger than the outer shape of the light emitting device 1 is
prepared, which is cut to size after providing cutting guide lines
28L along the outer edge of the light emitting device 1 while
reserving the ancillary sections 28. Also, the process for
producing the light emitting device 1F including creating through
holes 21 and 22 in alignment with the positions of the light
emitting sections 2 and the connectors 3 and 4, respectively, of
the flexible substrates 10, and achieving the reflective sheet 20F
by cutting in accordance with the finished product shape of the
light emitting device 1F including the ancillary sections 28. The
light emitting device 1F can otherwise be produced in similar
manner to in the case of the light emitting device 1. The through
holes 29 in the ancillary sections 28 at four corners of the
reflective sheet 20 may be formed as needed. The through holes 29
can be created at the same time the through holes 21 and 22 are
created.
In packaging the light emitting devices 1F, as shown in FIG. 11C,
the products (light emitting devices 1F) are stacked, and, for
example, stapled together at several locations in the ancillary
sections 28 so that the light emitting devices 1F may not shift. In
the cases where through holes 29 are provided in the ancillary
sections 28, the light emitting devices 1F can be bundled using
strings fed through the holes 29 so they may not shift. These light
emitting devices 1F may be then placed in a corrugated cardboard
box, for example. An insulating film may be laid over the outermost
surface of the stacked products.
Since the products (light emitting devices 1F) are held together
using the ancillary sections 28, shifting during transportation can
be reduced, which can reduce the occurrences of scratches
attributable to shifting of the products.
Following the transportation, the light emitting devices 1F may be
unpacked, removed the ancillary sections 28 along the cutting guide
lines 28L of the products (light emitting devices 1F), and used as
the regular light emitting devices 1 by users. In the case where
light emitting devices are packed in a corrugated cardboard box,
breaking or chipping at the edges of the light emitting devices may
occur. In the case of the light emitting device 1F, however, the
ancillary sections 28 which are the edges of the products and tend
to be damaged can be removed.
As explained above, according to the light emitting device 1F, even
using simple packaging way such as stacking and placing the
products (light emitting devices 1F) in a corrugated cardboard box,
(1) breaking and chipping of the edges of the product can be
reduced by removing the ancillary sections 28, and (2) the
occurrences of scratches can be reduced by reducing the products
from shifting during transportation.
By simplifying the packaging, the cost required for packaging can
be reduced even for a large area light emitting device 1 therefore
the price of the light emitting device can be reduced.
Embodiment 6
As shown in FIG. 12, the light emitting device 1G according to
Embodiment 6 differs from the light emitting device 1 according to
Embodiment such that the flexible substrates 10 are laminated with
the reflective sheet 20 disposed on the upper face 15 side and the
insulating sheet 50 disposed on the back face 16 side. The
insulating sheet 50 is continuously adhered to the faces of the
flexible substrates 10 opposite the upper faces 15 where the light
emitting sections 2 are disposed (i.e., the back faces 16), and the
same face of the reflective sheet 20 (the rear face 26) as that
adhering to the flexible substrates 10.
The insulating sheet 50 is preferably made of a synthetic resin,
such as polyethylene terephthalate (PET), or the like, a metal
sheet with insulating coating, or a metal sheet laminated with a
synthetic resin film, such as PET. The insulating sheet 50 is
formed larger than the flexible substrates 10, and when using a
single insulating sheet 50, it preferably has substantially the
same size as that of the reflective sheet 20. The thickness of the
insulating sheet 50 can be the same thickness as that of the
reflective sheet 20 in the case of the material of insulating sheet
50 is synthetic resin like PET. A plurality of insulating sheets
that are smaller in size than the reflective sheet 20 can be used
in the light emitting device 1G instead of one insulating sheet
50.
The light emitting device 1G can be produced by further performing
a step of providing the insulating sheet 50 following the
production of the light emitting device 1. More specifically, as
shown in FIG. 7D, the light emitting device 1 where the flexible
substrates 10 are adhered on the rear face 26 of the reflective
sheet 20 is prepared in advance. An adhesive member 30G, such as a
double-sided tape, is provided on one face of the insulating sheet
50 in advance. By adhered that face of the insulating sheet 50 to
the rear face 26 of the reflective sheet 20 with the adhesive
member 30G, the light emitting device 1G can be produced.
Alternatively, the adhesive member 30G may be provided on the rear
face 26 of the reflective sheet 20 first, followed by bonding the
insulating sheet 50 to the adhesive member 30G. A size, shape, and
the quantity of the adhesive member 30G may be suitably set.
According to the light emitting device 1G, the strength can be
increased.
Variation of Embodiment 6
The creepage distance as shown in FIGS. 5 and 6 is normally
required in order to ensure the insulating properties of the
flexible substrate 10 and 10a. In the case where the creepage
distances is eliminated by making an edge of the wiring pattern 13
and an edge of the base body 11 of the flexible substrates 10 or
10A substantially identical in a plan view, aside face of the
wiring member 13 will be bare on the edge of the flexible substrate
10 or 10A, which may raise a concern caused by static electricity
when handling the flexible substrates 10. In the light emitting
device 1G according to Embodiment 6, however, the flexible
substrates 10 are laminated with the reflective sheet 20 and the
insulating sheet 50, and thus the side faces of the wiring member
13 on the flexible substrates 10 will not be bare. Thus, the
flexible substrates 10 can be protected against static electricity
during the handling of the light emitting device 1 with the
flexible substrates 10, and insulating properties in the creepage
direction can be ensured at low cost by pasting the insulating
sheet 50 to the back faces 16 of the flexible substrates 10.
In a variation of Embodiment 6, as shown in FIG. 13, the flexible
substrate 10G has no creepage distances. As shown in FIG. 13, the
width of the flexible substrate 10G is denoted as W3. The width of
the wiring pattern 13 formed along a line in the longitudinal
direction of the flexible substrate 10G is denoted as L1, and the
creepage distance is 0. In this case, the relationship expressed by
the following formula (3) is established. The groove width between
the wiring members 13a, 13b, 13c is denoted as L3. W3=L1 formula
(3)
The flexible substrate 10G shown in FIG. 13 can be produced by
preparing a flexible substrate collective sheet 60 shown in FIG.
14, followed by separating them, for example. The collective sheet
60 shown here corresponds to ten flexible substrates. On each
substrate, the connector 3 is disposed at the left end, and the
connector 4 is disposed at the right end. In the collective sheet
60, the width of each of these ten flexible substrates, which will
be used as the flexible substrates 10G later is preset to the width
W3 shown in FIG. 13, i.e., the width L1 of the wiring pattern 13,
unlike the flexible substrates 10A.
By producing a collective sheet 60 designed as above, the width W3
of the flexible substrates 10G described above can be reduced, for
example, to a 60% value of the width W2 of the flexible substrate
10A shown in FIG. 6. The elimination of the creepage distances in
this way can reduce the areas of flexible substrates 10G, and thus
can reduce the production costs of the flexible substrates 10G.
Embodiment 7
As shown in FIGS. 15 and 16, the light emitting device 1H according
to Embodiment 7 differs from the light emitting device 1 according
to Embodiment 1 such that it is a double-side emitting type light
emitting device where light can be emitted from the rear face side.
The light emitting device 1H can produced by adhering the flexible
substrates 10 to the flexible substrates 10H via the adhesive
member 30. The light emitting device 1H can emit the light from the
light emitting sections 2 to both the front and rear faces side of
the light emitting device 1H. The flexible substrates 10H here have
similar configuration as that of the flexible substrates 10.
The light emitting device 1H can be produced by further performing
a step of bonding the flexible substrates 10H after producing a
light emitting device 1. For example, the light emitting device 1
in which the flexible substrates 10 are bonded on the rear face 26
of the reflective sheet 20, as shown in FIG. 7D, is prepared in
advance. A collective sheet of the flexible substrates 10H is
prepared in advance, and the adhesive member 30, such as a
double-sided tape, for example, is provided on the rear face of the
collective sheet. The light emitting device 1H can be produced by
bonding the back faces of the flexible substrates 10H, which have
been separated from the collective sheet, to the back faces 16 of
the flexible substrates 10 on the reflective sheet 20.
Alternatively, the adhesive member 30 may be first provided on the
back faces 16 of the flexible substrates 10 on the reflective sheet
20, followed by bonding the flexible substrates 10H to the adhesive
member 30.
According to the light emitting device 1H, a flexible double-sided
emission type light emitting device can be produced at low cost.
The light emitting device 1H, being a double-sided emission type,
can be applied to, for example, a double-sided internally
illuminated signboard where both the front and rear faces are
signboard faces illuminated by a light emitting device installed
inside.
Embodiment 8
The light emitting devices according to the embodiments preferably
further include a feature to reduce warping that can be caused by,
for example, temperature and/or humidity. As shown in FIG. 17, the
light emitting device 1K according to Embodiment 8 differs from the
light emitting device 1 according to Embodiment 1 by having a
reflective sheet 20K provided with broken-line shaped slits 70. The
slits 70 are provided to reduce warping resulting from, for
example, temperature and/or humidity. The slits 70 are created in
the direction substantially perpendicular to the upper face of the
flexible substrates 10 by perforating. A plurality of slits 70 are
created at positions that deviate from the light emitting sections
2 of the flexible substrates 10.
As for the slits, the distance between them, and the length and
width of, the holes (that is, slits 70) can be suitably selected
depending on the strength required of the light emitting device 1K
and within the ranges that can ensure the insulating properties of
the flexible substrates 10, for example. The slits are preferably
provided next to the light emitting sections 2 of the flexible
substrates 10. The slits may be formed at mid position between two
adjacent light emitting sections 2 located on flexible substrates
10, or a position that deviate from mid position. Moreover,
multiple slits may be created between two adjacent light emitting
sections 2 of the flexible substrates 10. The number of slits is
can be suitably selected. The sizes of the slits 70 may be common
to all or different. The spacing between the slits may be common to
all or different.
In producing the light emitting device 1K, a step of perforating
the unprocessed reflective sheet 20 is additionally performed prior
to disposing the adhesive member 30 on the reflective sheet 20.
More specifically, in the case where the reflective sheet 20 is
prepared as shown in FIG. 7A, multiple slits are vertically formed
while avoiding the positions of the light emitting sections 2 on
the flexible substrates 10. Thereafter, the device can be produced
in the same manner as in the case of the light emitting device
1.
In the case where the respective materials mentioned earlier are
used for the reflective sheet 20K and the flexible substrates 10 of
the light emitting device 1K, the reflective sheet 20K will have a
higher rate of heat shrinkage than the flexible substrates 10. For
example, under constant temperature and constant humidity
conditions, a member which the two materials having different rates
of heat shrinkage and coefficients of thermal expansion are bonded
tends to reveal different dimensional changes between the two
bonded materials, which may cause warping of the member. However,
the light emitting device 1K employs the reflective sheet 20K
provided with the slits 70, and thus warping can be reduced as the
gaps formed by the slits 70 expand when the reflective sheet 20K
shrinks due to temperature and/or humidity. According to the light
emitting device 1K, therefore, warping can be effectively reduced
even when the device is placed, for example, in a high-temperature
and high-humidity location, or is heated or dried.
Other Variations
In each of the embodiments discussed above, the reflective layer 8
formed on the flexible substrates 10 are disposed spaced apart from
the wiring pattern in the stacking direction by interposing the
underlayer 7. However, the underlayer 7 may not be disposed
immediately below the reflective layer 8, and the reflective layer
8 may be disposed directly on the wiring pattern.
Furthermore, the underlayer 7 may not be used, as each of the light
emitting devices according to the above embodiments can ensure the
insulating properties of the flexible substrates 10 using the
reflective sheet 20. In this case, the production costs of a large
area light emitting device can be further reduced.
In the light emitting devices according to the embodiments
discussed above, the connectors 3 and 4 on the flexible substrates
10 are connected to an external power supply using a wire harness.
However, a relay board provided with a wiring pattern can be
directly connected to the wiring member 13 by soldering, without
using the connectors 3 and 4. The relay board may be a general
circuit board, but is preferably an oblong flexible substrate. Such
a construction requires no wire harnesses or connectors, and thus
can reduce materials costs. This increases the cost reduction
effect particularly in the case where a large number of flexible
substrates are used.
INDUSTRIAL APPLICABILITY
The light emitting devices according to the embodiments described
in this disclosure can be used as various types of light sources
applicable to lighting fixtures, various indicators, automotive
lights, displays, liquid crystal display backlights, sensors,
traffic signals, automotive parts, signboard channel letters, and
the like.
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